For example, in semiconductor manufacturing processes, gases are sometimes supplied respectively from multiple introduction ports to a deposition chamber or the like at a predetermined flow rate ratio. The introduction ports are respectively provided with flow paths, and each of the flow paths is provided with a packaged fluid control device called a mass flow controller that controls the flow rate of a fluid flowing through the flow path (see Patent Literature 1).
Meanwhile, among gases used in semiconductor manufacturing processes, one toxic to human bodies and one whose chemical properties to human bodies are not well known exist, and such gases have to be prevented from leaking outside from pipes and the like constituting flow paths.
Accordingly, in order to prevent the pressure of the gas from being increased to result in leakage on the upstream side of the above-described mass flow controller, keeping the upstream side of the mass flow controller at, for example, a limit pressure lower than atmospheric pressure is stipulated as a requirement specification.
In response to such a requirement specification, the pressure on the upstream side is configured to be kept constant at a predetermined value lower than the limit pressure by providing a pressure regulator on the upstream side of the mass flow controller in the flow path.
However, in the case where the pressure on the upstream side of the mass flow controller is configured to be kept constant at the predetermined low pressure by the pressure regulator, the flow rate of the fluid to be supplied to the mass flow controller is in a limited state. For example, when an excessive set flow rate is set in the mass flow controller in the state where the supply of the fluid is limited as described, the convergence time required for a flow rate output to converge at the set flow rate becomes longer.